The present invention is generally related to roller bearings and is more particularly concerned with a failsafe mechanism for such bearings. The invention is especially intended for use in rotor control devices for helicopters.
Roller bearings are generally rugged, reliable devices having long operating lives. Nevertheless, in many cases occurrences of bearing failure may result from any of a number of causes. Lack of proper lubrication due to maintenance errors, failure of a lubrication system, fatigue in the bearing rollers or introduction of foreign objects or materials into the path of the bearing rollers may all produce severe problems in bearing operation and may ultimately cause complete failure of the bearing. Although rare, such bearing failure can have serious consequences with regard to the operation of equipment with which the bearing is utilized. Thus, despite the fact that the risk of bearing failure is generally acceptable there nevertheless are applications where effective means for dealing with or overcoming such failures are desirable or even imperative.
An example of such an application is in control devices for helicopter rotors. Bearings are used in connection with the swash plates and sliding sleeves of helicopter rotor control devices both in the main rotor and in the tail rotor of the helicopter. It will be apparent that failure of these parts could lead to failure of the helicopter controls and could possibly cause the helicopter to crash. Accordingly, the reliability of roller bearings used in such applications is of vital importance.
In the prior art, for example German Pat. No. 1,964,217, a device is known which operates to protect axial-radial roller bearings from destruction by overheating. Such bearings are usually arranged on a shaft between an adjusting nut and a shaft collar and they are rigidly braced against each other by means of the adjusting nut. The device also includes an interposed ring disk which consists of material that will melt or evaporate when the roller bearing becomes overheated. Due to the melting or evaporation of the ring disk, tension between the roller bearings is eliminated and a reduction of the temperature of the roller bearing may be expected.
However, prior art devices of this type are generally large in size and construction and in operation there may occur an intolerable degree of clearance between the parts due to the wetting or evaporation of the ring disk. As a result, the roller bearings will be only temporarily protected against over-heating if the lubrication system fails. In the event of prolonged failure of the lubrication system, seizing and dislodgement of the bearing rollers becomes unavoidable. Such known constructions would therefore be completely unsuitable for use in situations where the bearing rollers become fatigued or where foreign objects might tend to become lodged in the path of the rollers.
The present invention is therefore directed toward providing a device which will enable a roller bearing to continue to operate satisfactorily even after the bearing rollers seize.